This invention relates to improvements in methods and apparatus for removing hardened structural concrete from structures including steel-reinforced concrete structures. The invention is applicable, for example, in the repair of bridge spans and building structures by removing defective regions of concrete for replacements; also in the preparation of existing structures to make additions to them by removing old concrete in regions where joints are intended and also where reinforcing bars must be exposed for subsequent embedment in new concrete poured in constructing the addition. The invention is herein illustratively described by reference to its presently preferred embodiment and practice; however, it will be recognized that certain modifications and changes therein with respect to details may be made without departing from the essential features involved.
In the removal of hardened structural concrete from bridge spans and like structures it is, of course, highly important to avoid cutting into and damaging the reinforcing bars and also to avoid damaging the concrete in regions adjoining that to be removed. However, with the use of pneumatic jack hammers or similar tools, these requirements are difficult to satisfy in practice. The reinforcing bars, unpredictably located in most cases, are usually encountered by the jack hammer tool and perhaps damaged to some degree before the operator is aware of it. The clatter and vibration of a jack hammer accompanied by the accumulations of dust and concrete particles in the work area make it difficult for the operator to exercise very sensitive control over the cutting action on a continuing basis so as to avoid bar damage.
In addition, the repeated shocks of jack hammer blows can weaken the concrete in regions adjoining that initially designated for removal. This is especially the case in old structures wherein the concrete is brittle and often cracked by years of repeated load and thermal stress, the jack hammer blows often aggravating and extending such weaknesses. In addition, the repetition frequency of an air hammer tool can set up resonances in a concrete structure causing further damage. That such damage to adjoining concrete, involving enlarging and lengthening existing cracks and causing new ones, in serious in the conventional use of jack hammers has been determined by comparing results thereof with those achieved by the vibration-free technique of this invention. In general it is found that in like areas the actual amount of defective concrete that had to be removed with a jack hammer in order to pass inspection was considerably greater than that in the comparable case using the present invention. From these and other observations it is evident that use of a jack hammer type tool makes additional work for itself causing undesired job cost over-runs and often serious added damage to structures under repair. Yet jack hammers and other percussive tools, suffering these and other limitations and disadvantages, have still been regarded as essential heretofore for most jobs, especially the many where rotary cutters are impracticable.
With the foregoing and related considerations in view, a broad object of this invention is to provide an improved method and apparatus by which to remove volumes of hardened structural concrete over designated areas and to required depths both rapidly and efficiently, and to do so with precise removal dimensional control, without requiring an operator's constant close attention to tool action in the concrete, yet without causing incidental damage to the concrete in adjoining regions or to embedded reinforcing bars exposed in the removal process. With this invention the work area and the scanning jet nozzle system in action can be shielded for absorption of sound and shrouded for protective containment of loose particles and splashing water. Yet the resulting visual obscurement of the work area instantaneously involved presents no handicap or impediment to achieving the desired results.
A further object is to devise an improved technique for removing structural concrete, without the attendant problems of dust and noise pollution heretofore experienced; moreover, a process that is both efficient in terms of energy consumption per unit of work done, and relatively safe and less tiring and distasteful to attendant personnel.
Still another object hereof is to devise an improved apparatus and method to remove structural concrete safely and efficiently from around and beneath reinforcing bars and in the process thereof to scour the surfaces of the bars so as to remove corrosion and scale therefrom, preparing them for a better bond with new concrete, without cutting into and weakening the bar metal itself.